Our objective is to prevent falls in the elderly through exercise programs that maintain or increase leg strength. The specific aims of this proposal are: (1) to estimate the incidence of falls and attributable risk of falls due to leg weakness in older people who could potentially participate in muscle strengthening programs, (2) to characterize the relationship between leg muscle strength (knee flexors, knee extensors, ankle dorsiflexors, ankle plantarflexors) and falls, and (3) to assess whether simple clinical tests of leg strength can screen for patients at increased risk of falls due to leg weakness. The proposal seeks to answer certain questions relating to accomplishing the long-term goal: What is the potential of exercise programs to prevent falls? Which leg muscles should exercise programs strengthen, and how much? Are relative strengths of opposing muscle groups important? How can patients be identified whose risk of falls might be reduced through strength training? The study design combines a retrospective case control method and a prospective cohort method. The study will recruit a random sample of 130 patients age 65-85 from a HMO population of known size. Patients with known muscular disease and with contraindications to exercise will be excluded. The sample will be stratified on the basis of age, sex, and falls in the previous year (50% fallers, 50% nonfallers). Strength of the muscles controlling the knees and ankles will be measured at four different muscle velocities for each muscle group in both legs using a dynamometer. Dynamometer measurements and falls will be correlated with simple clinical tests of strength involving walking, standing, toe raises, and handgrip. Based on previous history of falls, a case control method will estimate how much leg weakness increases risk of falls. Because this retrospective method cannot determine whether weakness precedes or follows a fall, a cohort method will make a second estimate of the relative risk based upon prospective ascertainment of falls. Logistic analysis will control for potential confounding variables in the relationship of strength to falls, including abnormal gait, abnormal vision, overall health status, prescription drug use, and peripheral sensory nerve function. The study will test hypotheses that specific strength deficits are associated with falls. As some data suggests the hypothesized deficits are partly reversible, such research has direct implications for fall prevention.